1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus of an internal combustion engine which activates an exhaust gas purifying catalyst by increasing the quantity of fuel supplied to the internal combustion engine and supplying secondary air to an exhaust gas passage when the internal combustion engine is started.
2. Description of Related Art
As the exhaust gas purifying apparatus of the internal combustion engine, there has been well known an apparatus which at the time of a cold starting, increases the quantity of fuel supplied to the internal combustion engine and introduces the second air into an exhaust gas passage in order to activate an exhaust gas purifying catalyst rapidly and if catalyst temperature exceeds a predetermined temperature, stops introduction of the secondary air and increase of fuel accompanying the introduction (see Japanese Patent Application Laid-Open (JP-A) No. 9-103647). In addition to this, there exist JP-A Nos. 4-231649 and 2000-352345 as preceding technology documents of the present invention.
To activate catalyst by introducing the secondary air, it is necessary to control the secondary air-fuel ratio, which is given as a mass ratio between air and fuel near the catalyst into the range appropriate for warm-up of the catalyst (for example, near 16). If the secondary air-fuel ratio deflects to the lean side with respect to the appropriate range, the warm-up of the catalyst delay due to cooling effect of the catalyst due to the secondary air and reduction of oxidation thereby worsening emission of exhaust gas while if it deflects to the rich side, there is a fear that thermal deterioration or melting loss due to overheat of the catalyst may be induced because of intensification in oxidation.
Because the second air-fuel ratio near the catalyst is correlated to primary air-fuel ratio given as a mass ratio between intake air and fuel in a combustion chamber, the primary air-fuel ratio needs to be evident as a premise for controlling the secondary air-fuel ratio. However, in an actual internal combustion engine, because the primary air-fuel ratio deflects due to an error in the quantity of intake air, a deviation of the fuel amount from a control instruction value to the fuel injection valve and the like, the primary air-fuel ratio is learnt by using an air-fuel ratio sensor or the like and the primary air-fuel ratio is so controlled to coincide with a control target value based on that learning result. Even at the time of starting the internal combustion engine, new leaning is sometimes executed because previous learning results cannot be used due to battery clear or initialization of the learning results accompanying errors in the SRAM which stores the learning results. In this case, the primary air-fuel ratio cannot be grasped accurately until the learning is completed, and as a result, the secondary air-fuel ratio deflects from its appropriate range, so that the above-described problem may occur. Further, even if there is a learning result usable when the internal combustion engine starts, that learning result may be not reliable due to a fault in the air-fuel ratio sensor or the like and in such a case, the above-described problem may occur regarding the secondary air-fuel ratio.